III2 Appendix VI. two wedge-like projections B. The pull of the chain causes these to lie firmly in the tooth space, as at c, when new. After wear, the chain rides up the teeth in the manner shewn at b until it finds its bearing, but it will be noticed that the meeting surface of link and tooth has a constant angle to the line of pull. The lower view indicates the appearance after the chain has stretched or Refold PxJbch, -chain,. 976. worn *6 in. per foot, before which it would have been adjusted. On account of its perfect action the chain has been used in the Wolseley motor-car with great satisfaction for the very rapid drive direct from the engine, its speed reaching 800 to 1200 ft. per min. The construction of the chain requires one of the wheels to be shrouded both sides so as to hold it in place, and for this purpose the smaller wheel is chosen as a matter of cheapness. P. 550. The Dynamo. Elementary Printipks-.—A 'conductor' is any material that will conduct electricity. Applying the term to dynamo work, it may be viewed as a rod or wire of copper arranged to cut or pass across the lines of force of a magnetic field.